Most recently developed survival lamp units for use on personal flotation devices, such as inflatable life vests, require a water-responsive switch closing an electric circuit between a battery and a light source when in contact with a coherent mass of water. A typical water-responsive switch comprises a pair of electric terminals impressed with a certain voltage potential. When in the dry state, the impedence between the terminals is very high and the current allowed to circulate is virtually nil. However, when wet, the impedence is dramatically reduced establishing an electrical path which sets a simple transistor circuit in the conduction state, closing the electric circuit between the battery and the light source.
A major drawback of this type of water-responsive switches is the requirement to maintain the electric terminals continually immersed in water to obtain a steady operation of the light source. Any discontinuance in the electrical path between the terminals will extinguish the light source. Consequently, when used on a life vest or on another type of flotation device, the water-responsive switch and the light source of the survival lamp unit must be physically separated to locate these components below and above the water line respectively, for a proper operation. This requirement complicates the construction of the life vest because the manufacturer must provide a routing for the cable interconnecting the two components, an underwater pocket to hold the water-responsive switch and in addition, the likelihood of lamp failure is increased because of possible leaks at the cable/component junctions.